The only thing I can think of is

Changed
(1) CallingConvention.StdCall
(2) Use IntPtr for the dll return value, then convert IntPtr to string

 //declare string Invoke1 in (addbs(justpath(.cProgramPath)) + "ww_local.dll") as ww_localInvoke string cInvokeString

        [DllImport(@"C:\Program Files (x86)\Siriusware\Pool\ww_local.dll", 
            ExactSpelling = false, 
            CallingConvention = CallingConvention.StdCall, 
            CharSet = CharSet.Auto)]
        static extern IntPtr Invoke1([MarshalAs(UnmanagedType.LPTStr)] String str);

then

string translate  = Marshal.PtrToStringAuto(Invoke1(invoke));

return translate ;